I recently came across a study published this year in the Archives of Internal Medicine looking at the association between sleep habits and susceptibility to the common cold.

In this study, 153 healthy men and women between the ages of 21-55 were asked to record their sleep duration and sleep efficiency (the amount of time they actually slept divided by the amount of time in bed) on a daily basis for 14 days. At the end of this period, they were placed in isolation, and given nose drops containing rhinovirus, the virus which causes the common cold. Cold symptoms were monitored starting one day prior to exposure and during each of the 5 days following exposure to the cold virus.

66 participants (43%) developed a cold following exposure to the virus. The researchers found that those study participants who slept fewer than 7 hours/night on average during the 14 days preceding the exposure were almost three times more likely to develop clinical signs of a cold than those who slept 8 or more hours/night on average during that time. Likewise, people with sleep efficiency less than 92% were five and a half times more likely to get sick than those whose sleep efficiency was greater than 98%. The differences in developing a cold could not be explained by differences in levels of antibodies to the cold virus, the season, the participants' body weight relative to height, age, or socioeconomic status. There was no correlation between whether a participant reported feeling well rested after a night's sleep and whether or not s/he became infected.